MDEV-19869 Port innodb_fts.fulltext2 from mysql to mariadb.

- Ported mysql Bug#20597981 test case to mariadb-10.2
- InnoDB never used fts_doc_id_in_read_set. Basically it tells
innodb to read the fts_doc_id from the index record itself.

mysql-test/suite/innodb_fts/r/fulltext2.result

@@ -242,3 +242,33 @@ a
 „MySQL“
 DROP TABLE t1;
 SET NAMES latin1;
+CREATE TABLE t1 (
+FTS_DOC_ID BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
+id int(10) not null ,
+first_name varchar(50) NOT NULL,
+last_name varchar(50) NOT NULL,
+PRIMARY KEY (FTS_DOC_ID),
+UNIQUE KEY idx_1 (first_name, last_name),
+FULLTEXT KEY `idx_2` (first_name)
+) ENGINE=InnoDB;
+INSERT INTO t1 (id, first_name, last_name) VALUES
+(10, 'Bart', 'Simpson'),
+(11, 'Homer', 'Simpson'),
+(12, 'Marge', 'Simpson'),
+(13, 'Lisa', 'Simpson'),
+(14, 'Maggie', 'Simpson'),
+(15, 'Ned', 'Flanders'),
+(16, 'Nelson', 'Muntz');
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+SELECT fts_doc_id, first_name, last_name, MATCH(first_name) AGAINST('Homer' IN BOOLEAN MODE) AS score FROM t1;
+fts_doc_id	first_name	last_name	score
+1	Bart	Simpson	0
+2	Homer	Simpson	0.7141907215118408
+4	Lisa	Simpson	0
+5	Maggie	Simpson	0
+3	Marge	Simpson	0
+6	Ned	Flanders	0
+7	Nelson	Muntz	0
+DROP TABLE t1;

mysql-test/suite/innodb_fts/t/fulltext2.test

@@ -11,11 +11,6 @@
 DROP TABLE IF EXISTS t1;
 --enable_warnings
 
-if (`select plugin_auth_version <= "5.6.10" from information_schema.plugins where plugin_name='innodb'`)
-{
-  --skip Not fixed in InnoDB 5.6.10 or earlier
-}
-
 CREATE TABLE t1 (
   i int(10) unsigned not null auto_increment primary key,
   a varchar(255) not null,
@@ -239,3 +234,29 @@ INSERT INTO t1 VALUES('„MySQL“');
 SELECT a FROM t1 WHERE MATCH a AGAINST('“MySQL„' IN BOOLEAN MODE);
 DROP TABLE t1;
 SET NAMES latin1;
+
+#
+# Bug #20597981 - WRONG RELEVANCE RANKING FOR FULL TEXT SEARCHES
+# WHEN FTS_DOC_ID IS PRIMARY KEY
+CREATE TABLE t1 (
+  FTS_DOC_ID BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
+  id int(10) not null ,
+  first_name varchar(50) NOT NULL,
+  last_name varchar(50) NOT NULL,
+  PRIMARY KEY (FTS_DOC_ID),
+  UNIQUE KEY idx_1 (first_name, last_name),
+  FULLTEXT KEY `idx_2` (first_name)
+) ENGINE=InnoDB;
+
+INSERT INTO t1 (id, first_name, last_name) VALUES
+(10, 'Bart', 'Simpson'),
+(11, 'Homer', 'Simpson'),
+(12, 'Marge', 'Simpson'),
+(13, 'Lisa', 'Simpson'),
+(14, 'Maggie', 'Simpson'),
+(15, 'Ned', 'Flanders'),
+(16, 'Nelson', 'Muntz');
+
+analyze table t1;
+SELECT fts_doc_id, first_name, last_name, MATCH(first_name) AGAINST('Homer' IN BOOLEAN MODE) AS score FROM t1;
+DROP TABLE t1;

storage/innobase/handler/ha_innodb.cc

@@ -9688,14 +9688,16 @@ ha_innobase::change_active_index(
 	since FT search returns rank only. In addition engine should
 	be able to retrieve FTS_DOC_ID column value if necessary. */
 	if ((m_prebuilt->index->type & DICT_FTS)) {
-#ifdef MYSQL_STORE_FTS_DOC_ID
-		if (table->fts_doc_id_field
-		    && bitmap_is_set(table->read_set,
-				     table->fts_doc_id_field->field_index
-				     && m_prebuilt->read_just_key)) {
-			m_prebuilt->fts_doc_id_in_read_set = 1;
+
+		for (ulint i = 0; i < table->s->fields; i++) {
+			if (m_prebuilt->read_just_key
+			    && bitmap_get_next_set(table->read_set, i)
+			    && !strcmp(table->s->field[i]->field_name,
+				       FTS_DOC_ID_COL_NAME)){
+				m_prebuilt->fts_doc_id_in_read_set = true;
+				break;
+			}
 		}
-#endif
 	} else {
 		dtuple_set_n_fields(m_prebuilt->search_tuple,
 				    m_prebuilt->index->n_fields);
@@ -9706,13 +9708,12 @@ ha_innobase::change_active_index(
 
 		/* If it's FTS query and FTS_DOC_ID exists FTS_DOC_ID field is
 		always added to read_set. */
-
-#ifdef MYSQL_STORE_FTS_DOC_ID
-		m_prebuilt->fts_doc_id_in_read_set =
-			(m_prebuilt->read_just_key && table->fts_doc_id_field
-			 && m_prebuilt->in_fts_query);
-#endif
-
+		m_prebuilt->fts_doc_id_in_read_set = m_prebuilt->in_fts_query
+			&& m_prebuilt->read_just_key
+			&& dict_index_contains_col_or_prefix(
+					m_prebuilt->index,
+					m_prebuilt->table->fts->doc_col,
+					false);
 	}
 
 	/* MySQL changes the active index for a handle also during some